C# C# Collections Arrays Jagged Arrays

William Wendell
William Wendell
904 Points

What does "Object reference not set to an instance of an object" mean?

doesn't accept the code I have despite having what seems to be the right answer

Math.cs
namespace Treehouse.CodeChallenges
{
    public static class MathHelpers
    {
       // private int MaxFactor {get;set;}
       // private int [][] Array = new int[MaxFactor][];

        public static int[][] BuildMultiplicationTable(int maxFactor)
        {
            //MaxFactor = maxFactor;
            int[][] array = new int[maxFactor][];

            for(int i = 0; i < array.Length; i++)
            {
                for(int j = 0; j < maxFactor; j++)
                    array[i][j] = i * j;
            }
            return array;
        }
    }

    //public class Arrays
    //{
      //  public int[][]
    //}
}

1 Answer

James Churchill
STAFF
James Churchill
Treehouse Teacher

William,

The error "Object reference not set to an instance of an object" means that you're encountering a "null" value at runtime when you're expecting an object. I would double check how you're initializing the jagged array.

Sometimes I find it helpful to read Microsoft's official documentation on their MSDN website. Check out this page about jagged arrays.

Jagged Arrays (C# Programming Guide) https://msdn.microsoft.com/en-us/library/2s05feca.aspx

Thanks ~James